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(a) A pure substance consists of only one type of element or compound, whereas a mixture consists of two or more different substances not chemically joined together. (b) The filter paper has tiny pores that allow liquid water molecules to pass through, but the larger particles of insoluble sand cannot pass through and are left behind as residue on the paper. (c) Rf = distance moved by spot / distance moved by solvent front = 5.4 / 9.0 = 0.60. (d) Entering at the bottom ensures the condenser jacket is completely filled with cold water, which provides maximum cooling and efficient condensation of the vapour throughout the tube.

Part (a) [2 marks]: 1 mark for stating that a pure substance contains only one substance/element/compound. 1 mark for stating that a mixture contains two or more different substances (not chemically joined). Part (b) [2 marks]: 1 mark for stating that filter paper has small holes/pores that let liquid/water through. 1 mark for stating that insoluble solid/sand particles are too large to pass through. Part (c) [3 marks]: 1 mark for correct formula (Rf = distance moved by spot / distance moved by solvent). 1 mark for correct substitution (5.4 / 9.0). 1 mark for correct calculation (0.60 or 0.6). Part (d) [3 marks]: 1 mark for stating it ensures the outer jacket is completely filled with cold water. 1 mark for stating it maximises heat transfer / cooling effect. 1 mark for linking this to efficient condensation of vapour back into liquid.

(a) (i) +1, (ii) 0, (iii) -1. (b) Protons = 17, Electrons = 17, Neutrons = 35 - 17 = 18. (c) Relative atomic mass = \(((69.0 \times 63) + (31.0 \times 65)) / 100 = (4347 + 2015) / 100 = 6362 / 100 = 63.6\).

Part (a) [3 marks]: 1 mark for proton is +1. 1 mark for neutron is 0. 1 mark for electron is -1. Part (b) [3 marks]: 1 mark for 17 protons. 1 mark for 17 electrons. 1 mark for 18 neutrons. Part (c) [4 marks]: 1 mark for multiplying each mass by its percentage: (69.0 * 63) and (31.0 * 65). 1 mark for adding these values together: 4347 + 2015 = 6362. 1 mark for dividing by 100: 63.62. 1 mark for rounding to 1 decimal place: 63.6.

(a) (i) Red, (ii) Purple / Violet. (b) (i) Effervescence (bubbling/fizzing) and the zinc powder dissolves / temperature increases. (ii) zinc + sulfuric acid -> zinc sulfate + hydrogen. (iii) Collect the gas in a test tube, apply a burning splint, and it will burn with a squeaky pop sound. (c) Hydrochloric acid fully ionises (or dissociates) in aqueous solution to release hydrogen ions, whereas ethanoic acid only partially ionises.

Part (a) [2 marks]: 1 mark for Red (for pH 1). 1 mark for Purple / Violet (for pH 14). Part (b) [6 marks]: (i) 2 marks for any two observations from: bubbling/fizzing/effervescence, zinc solid disappearing/dissolving, mixture heating up. (ii) 2 marks for: zinc + sulfuric acid -> zinc sulfate + hydrogen (1 mark for reactants, 1 mark for products). (iii) 2 marks: Apply a lit/burning splint (1 mark), squeaky pop sound heard (1 mark). Part (c) [2 marks]: 1 mark for stating hydrochloric acid fully ionises/dissociates. 1 mark for stating ethanoic acid only partially ionises/dissociates.

(a) The correct order from most to least reactive is: sodium, iron, copper, gold. (b) (i) iron oxide + carbon -> iron + carbon dioxide (or carbon monoxide). (ii) Carbon is more reactive than iron, so it can displace iron from its oxide, but carbon is less reactive than aluminium, so it cannot displace aluminium from aluminium oxide. (iii) Iron oxide is reduced because it loses oxygen to form iron. (c) Recycling saves a huge amount of electrical energy, conserves the raw resource (bauxite ore), and reduces greenhouse gas emissions and environmental damage from mining.

Part (a) [2 marks]: 2 marks for correct order: sodium, iron, copper, gold (1 mark if only one metal is out of position). Part (b) [6 marks]: (i) 2 marks for: iron oxide + carbon -> iron + carbon dioxide (accept carbon monoxide) (1 mark for reactants, 1 mark for products). (ii) 2 marks: 1 mark for stating carbon is more reactive than iron, 1 mark for stating carbon is less reactive than aluminium. (iii) 2 marks: 1 mark for identifying iron oxide, 1 mark for explaining it loses oxygen. Part (c) [2 marks]: 2 marks for any two advantages from: saves energy / uses less electricity, conserves raw resources / bauxite, reduces mining / land damage, reduces CO2 emissions.

(a) (i) The electronic configuration of oxygen is 2,6. (ii) Two oxygen atoms share two pairs of electrons (double bond) in the overlapping region. Each atom has 4 non-bonding outer electrons remaining. (b) (i) Each magnesium atom loses 2 electrons to form a Mg2+ ion. Each oxygen atom gains 2 electrons to form an O2- ion. These oppositely charged ions attract each other. (ii) Magnesium oxide has a giant ionic lattice structure with strong electrostatic forces of attraction between the oppositely charged ions, requiring a large amount of energy to break.

Part (a) [4 marks]: (i) 1 mark for 2,6. (ii) 3 marks: 1 mark for two shared pairs of electrons in the overlap (double bond). 1 mark for 4 non-bonding electrons on each oxygen atom. 1 mark for two circles overlapping with correct symbols. Part (b) [6 marks]: (i) 4 marks: 1 mark for magnesium losing electrons. 1 mark for losing exactly 2 electrons. 1 mark for oxygen gaining electrons. 1 mark for gaining exactly 2 electrons (or transfer of 2 electrons from Mg to O). (ii) 2 marks: 1 mark for mentioning giant ionic lattice with strong electrostatic attraction between oppositely charged ions. 1 mark for stating it requires a lot of energy to overcome / break.

(a) An electrolyte is a liquid or solution that contains ions and conducts electricity. (b) (i) Lead is formed at the cathode. (ii) Bromine is formed at the anode. (c) (i) Chlorine gas, (ii) Hydrogen gas, (iii) Sodium hydroxide. (d) In solid sodium chloride, the ions are held in fixed positions in a giant lattice and cannot move. In sodium chloride solution, the lattice is broken down, so the ions are free to move and carry the electric charge.

Part (a) [1 mark]: 1 mark for a liquid/solution containing ions that conducts electricity. Part (b) [2 marks]: (i) 1 mark for Lead. (ii) 1 mark for Bromine. Part (c) [3 marks]: (i) 1 mark for Chlorine. (ii) 1 mark for Hydrogen. (iii) 1 mark for Sodium hydroxide. Part (d) [4 marks]: 1 mark for stating solid has a giant lattice structure with ions in fixed positions. 1 mark for stating ions cannot move in solid. 1 mark for stating in solution, ions are free to move. 1 mark for stating they carry the electric current / charge.

(a) The symbol represents a reversible reaction. (b) (i) Nitrogen is obtained from the air. Hydrogen is obtained from natural gas (or steam reforming of methane). (ii) Temperature: 450 degrees C, Pressure: 200 atmospheres (atm), Catalyst: Iron. (c) (i) Sulfuric acid and ammonia solution (ammonium hydroxide). (ii) ammonia + sulfuric acid -> ammonium sulfate.

Part (a) [1 mark]: 1 mark for reversible reaction. Part (b) [5 marks]: (i) 2 marks: 1 mark for nitrogen from air, 1 mark for hydrogen from natural gas / methane / steam. (ii) 3 marks: 1 mark for temperature of 450 °C (accept 400 - 500 °C), 1 mark for pressure of 200 atm (accept 150 - 250 atm), 1 mark for iron catalyst. Part (c) [4 marks]: (i) 2 marks: 1 mark for sulfuric acid, 1 mark for ammonia (accept ammonium hydroxide). (ii) 2 marks for: ammonia + sulfuric acid -> ammonium sulfate (1 mark for reactants, 1 mark for product).

(a) (i) Oxygen and water. (ii) Hydrated iron(III) oxide. (b) Galvanising coats the iron with zinc. Zinc acts as a barrier, preventing water and oxygen from reaching the iron. If scratched, zinc is more reactive than iron, so it reacts/corrodes preferentially (sacrificial protection) to protect the iron. (c) (i) Pure copper has regular layers of atoms of the same size that can easily slide over each other. Brass has zinc atoms of a different size, which disrupt the regular layers and prevent them from sliding easily. (ii) Transition metals have higher densities / higher melting points / form coloured compounds / can act as catalysts.

Part (a) [3 marks]: (i) 2 marks: 1 mark for oxygen / air, 1 mark for water / moisture. (ii) 1 mark for hydrated iron(III) oxide (accept iron oxide). Part (b) [3 marks]: 1 mark for stating zinc acts as a barrier (preventing oxygen/water from reaching iron). 1 mark for stating zinc is more reactive than iron. 1 mark for stating zinc corrodes/reacts instead of iron (sacrificial protection). Part (c) [4 marks]: (i) 3 marks: 1 mark for stating pure copper has regular layers of atoms of the same size. 1 mark for stating these layers slide over each other easily. 1 mark for stating zinc atoms have a different size, disrupting the layers / preventing sliding. (ii) 1 mark for any correct property, e.g., high density, high melting point, hard/strong, forms coloured compounds, catalytic activity.

(a) The reaction between an acid and a metal oxide is neutralisation. (b) Excess copper oxide is added to ensure all the sulfuric acid is completely reacted and neutralised, so no unreacted acid remains in the final solution. (c) The mixture is filtered using a funnel and filter paper. The excess insoluble copper oxide remains on the paper as residue, while the copper sulfate solution passes through as filtrate. (d) To obtain dry crystals, heat the copper sulfate solution in an evaporating basin to evaporate some of the water and concentrate the solution. Leave the concentrated solution to cool so crystals form. Filter the crystals and pat them dry with filter paper. (e) The word equation is: copper oxide + sulfuric acid \(\rightarrow\) copper sulfate + water. (f) A strong dilute acid like sulfuric acid has a pH in the range of 0 to 3.

(a) 1 mark: neutralisation. (b) 1 mark: to make sure all the acid reacts / is neutralised. (c) 1 mark: filtration / filtering. 1 mark: detail of filtration (e.g. using filter paper and funnel / copper oxide is residue). (d) 1 mark: heat / evaporate (some of) the water. 1 mark: leave to cool / crystallise. 1 mark: dry the crystals (with filter paper / in a warm oven). (e) 1 mark: copper oxide + sulfuric acid on left of arrow. 1 mark: copper sulfate + water on right of arrow. (f) 1 mark: any value from 0 to 3 (accept 'less than 7').

(a)(i) The apparatus is a condenser (or Liebig condenser). (ii) Cold water is circulated through the outer glass jacket of the condenser. This cools the inner glass tube so that the hot water vapour passing through it loses thermal energy and condenses back into liquid water. (iii) The change of state is evaporation (or boiling/vaporisation). (b)(i) Pencil graphite is insoluble in the solvent and will not run or smear. Ink is soluble and would dissolve, moving up the paper and interfering with the chromatography results. (ii) The Rf value is calculated using the formula: \(R_f = \frac{\text{distance travelled by spot}}{\text{distance travelled by solvent}}\). Substituting the values: \(R_f = \frac{4.2}{7.0} = 0.6\). (iii) If the food dye is a mixture, the chromatogram will show more than one spot (multiple spots) separated vertically from the starting line.

(a)(i) 1 mark: condenser / Liebig condenser. (a)(ii) 1 mark: cold water flows through the outer jacket. 1 mark: this cools the inner tube / vapour condenses. (a)(iii) 1 mark: evaporation / boiling / vaporisation. (b)(i) 1 mark: pencil is insoluble / will not run. 1 mark: ink is soluble / would run / would interfere with results. (b)(ii) 1 mark: correct working/formula (\(4.2 / 7.0\)). 1 mark: 0.6. (b)(iii) 1 mark: produces more than one spot / multiple spots. 1 mark: spots are at different heights / separated.

Part (a): Crude oil consists mainly of hydrocarbons, which are compounds containing only hydrogen and carbon. Part (b): First, the crude oil is heated in a furnace until it vaporises. The vapour is then piped into the bottom of a fractionating column, which has a temperature gradient (hotter at the bottom, cooler at the top). As the vapours rise up the column, different hydrocarbons condense at different levels where the temperature falls below their specific boiling points. The fractions are then continuously tapped off. Part (c): Kerosene is the specific fraction used as fuel for aircraft (jet fuel). Part (d)(i): Saturated means the carbon atoms are joined by single covalent bonds only (no double carbon-carbon bonds are present). Part (d)(ii): Alkanes follow the general formula \(C_nH_{2n+2}\). Part (d)(iii): Using the general formula with \(n = 5\), the number of hydrogen atoms is \(2 \times 5 + 2 = 12\). Therefore, the molecular formula is \(C_5H_{12}\).

Part (a): 1 mark for hydrocarbons. Part (b): 1 mark for heating/vaporising crude oil; 1 mark for mentioning the temperature gradient of the column (hot at the bottom, cooler at the top); 1 mark for vapours rising and condensing; 1 mark for condensing at different levels/boiling points. Part (c): 1 mark for kerosene. Part (d)(i): 1 mark for only single (C-C) bonds / no double bonds. Part (d)(ii): 1 mark for \(C_nH_{2n+2}\). Part (d)(iii): 2 marks for \(C_5H_{12}\) (1 mark for C5, 1 mark for H12).

Part (a): Group 1 elements are known as the alkali metals. Part (b)(i): When sodium reacts with water, it floats because it is less dense than water, melts into a shiny ball due to the heat produced, moves rapidly across the water surface, and fizzes (effervesces) as hydrogen gas is produced. Part (b)(ii): The universal indicator turns blue or purple because the reaction produces sodium hydroxide, which is an alkaline solution. Part (c): The word equation is: sodium + water -> sodium hydroxide + hydrogen. Part (d): Potassium has an electronic configuration of 2.8.8.1, whereas sodium is 2.8.1. Potassium has more electron shells, meaning its single outer electron is further from the positive nucleus and experiences more shielding. Therefore, the outer electron is less strongly attracted to the nucleus and is lost more easily, making potassium more reactive.

Part (a): 1 mark for 'alkali metals'. Part (b)(i): 3 marks for any three correct observations (floats / melts into a ball / fizzes or bubbles / moves rapidly / gets smaller and disappears). Part (b)(ii): 1 mark for stating blue or purple; 1 mark for explaining that an alkaline solution (or sodium hydroxide) is formed. Part (c): 1 mark for reactants (sodium + water); 1 mark for products (sodium hydroxide + hydrogen). Part (d): 1 mark for identifying that potassium has more shells / outer electron is further from the nucleus; 1 mark for explaining that the outer electron is lost more easily.

Part (a)(i): The missing product is carbon dioxide, \(\text{CO}_2\). Part (a)(ii): Place the calcium carbonate and hydrochloric acid in a conical flask, immediately seal with a stopper connected via a delivery tube to a gas syringe (or an inverted measuring cylinder filled with water). Start a stopwatch and record the volume of gas collected at set intervals (e.g., every 10 seconds). Part (b)(i): Using powder increases the rate of reaction. Part (b)(ii): Powder has a larger surface area to volume ratio than large chips, exposing more reactant particles. This results in a higher frequency of successful collisions per second. Part (c): Increasing the temperature increases the rate of reaction. This is because particles gain thermal energy and convert it to kinetic energy, moving faster and colliding more frequently. Additionally, more particles have energy greater than or equal to the activation energy, making a higher percentage of collisions successful.

Part (a)(i): 1 mark for \(\text{CO}_2\) (accept carbon dioxide). Part (a)(ii): 1 mark for using a gas syringe or inverted cylinder; 1 mark for measuring volume of gas; 1 mark for recording at timed/regular intervals. Part (b)(i): 1 mark for increased rate of reaction. Part (b)(ii): 1 mark for larger surface area; 1 mark for more frequent collisions. Part (c): 1 mark for stating rate increases; 1 mark for more frequent collisions; 1 mark for more collisions having energy greater than or equal to the activation energy (more successful collisions).

Part (a)(i): The early atmosphere consisted mostly of carbon dioxide and water vapour, with small amounts of nitrogen, methane, and ammonia. Part (a)(ii): As the Earth cooled down below the boiling point of water, water vapour in the atmosphere condensed into liquid water, which gathered in depressions on the Earth's crust to form the oceans. Part (b)(i): Carbon dioxide levels decreased because plants used carbon dioxide for photosynthesis. Part (b)(ii): Oxygen levels increased because oxygen is released as a product of photosynthesis. Part (c): Short wavelength electromagnetic radiation (such as ultraviolet and visible light) from the Sun passes through the greenhouse gases in the atmosphere to reach the Earth's surface. The Earth's surface absorbs this energy and warms up. The warm surface then re-radiates energy as longer wavelength infrared (thermal) radiation. Greenhouse gases absorb this longer wavelength infrared radiation, preventing it from escaping into space, and re-emit it in all directions, keeping the planet warm.

Part (a)(i): 2 marks for any two correct gases (carbon dioxide, water vapour, nitrogen, methane, ammonia). Part (a)(ii): 1 mark for Earth cooling; 1 mark for water vapour condensing into liquid water. Part (b)(i): 1 mark for carbon dioxide. Part (b)(ii): 1 mark for oxygen. Part (c): 1 mark for short wavelength radiation passing through the atmosphere; 1 mark for the Earth's surface absorbing and warming up; 1 mark for the Earth emitting longer wavelength/infrared radiation; 1 mark for greenhouse gases absorbing this long wavelength radiation and keeping heat in the atmosphere.

Part (a): \(M_r(\text{CuSO}_4) = A_r(\text{Cu}) + A_r(\text{S}) + 4 \times A_r(\text{O}) = 63.5 + 32 + (4 \times 16) = 63.5 + 32 + 64 = 159.5\). Part (b): Total mass of oxygen in \(\text{CuSO}_4\) is \(4 \times 16 = 64\). Percentage by mass of oxygen = \(\frac{64}{159.5} \times 100 = 40.13\%\). Part (c)(i): Moles of magnesium (Mg) = \(\frac{\text{mass}}{A_r} = \frac{1.2}{24} = 0.05\text{ mol}\). According to the equation, 2 moles of Mg produce 2 moles of MgO, which is a 1:1 molar ratio. So, moles of MgO produced = 0.05 mol. \(M_r(\text{MgO}) = 24 + 16 = 40\). Mass of MgO = \(\text{moles} \times M_r = 0.05 \times 40 = 2.0\text{ g}\). Part (c)(ii): Reasons include: the reaction is incomplete, some product is left behind in the crucible or lost during transfer, or some reactants underwent alternative side reactions.

Part (a): 2 marks for 159.5 (1 mark for correct working: 63.5 + 32 + 64). Part (b): 2 marks for 40.13% (accept 40% or 40.1%) (1 mark for showing division by 159.5). Part (c)(i): 4 marks total: 1 mark for calculating moles of Mg (0.05); 1 mark for using 1:1 ratio to identify moles of MgO (0.05); 1 mark for calculating Mr of MgO (40); 1 mark for final mass of 2.0 g. Part (c)(ii): 2 marks for any two valid reasons (e.g., incomplete reaction / product lost during handling / side reactions).

Part (a)(i): Group 7 elements are commonly called the halogens. Part (a)(ii): Bromine is a liquid at room temperature and has a distinctive red-brown color. Part (b)(i): When chlorine displaces iodine, a brown solution of iodine is formed, causing a visible color change from colorless to brown. Part (b)(ii): Chlorine gas reacts with iodide ions: \(\text{Cl}_2(\text{g}) + 2\text{I}^-(\text{aq}) \rightarrow 2\text{Cl}^-(\text{aq}) + \text{I}_2(\text{aq})\). Part (b)(iii): Chlorine is more reactive than iodine because it has fewer electron shells and a smaller atomic radius. This means the incoming electron experiences less shielding and is more strongly attracted to the positive nucleus, making it easier for chlorine to gain an electron. Part (c): To test for chlorine gas, hold damp blue litmus paper over the gas source. The paper will briefly turn red (as chlorine forms acidic HCl in the dampness) and then quickly bleaches white.

Part (a)(i): 1 mark for halogens. Part (a)(ii): 1 mark for liquid; 1 mark for red-brown. Part (b)(i): 1 mark for the solution turning brown (accept yellow/brown). Part (b)(ii): 2 marks for \(\text{Cl}_2 + 2\text{I}^- \rightarrow 2\text{Cl}^- + \text{I}_2\) (1 mark for correct formulas, 1 mark for balancing). Part (b)(iii): 1 mark for stating chlorine is more reactive than iodine; 1 mark for explaining that chlorine gains an electron more easily. Part (c): 1 mark for using damp blue litmus paper; 1 mark for showing it is bleached white (turns white).

Part (a)(i): A chemical reaction that absorbs heat energy from the surroundings, resulting in a temperature drop, is called an endothermic reaction. Part (a)(ii): On a reaction profile diagram for an endothermic reaction, the energy level of the reactants is lower than the energy level of the products. A curve is drawn connecting them that rises to a peak. The activation energy is represented as a vertical arrow pointing upwards from the reactants' energy level to the highest point (peak) of the curve. Part (b)(i): Breaking chemical bonds in reactants is an endothermic process (requires energy input). Making chemical bonds in products is an exothermic process (releases energy). A reaction is overall exothermic when the total energy released during bond making is greater than the total energy absorbed during bond breaking. Part (b)(ii): Overall energy change = Energy needed to break bonds - Energy released making bonds = 1500 - 2100 = -600 kJ/mol. Because the overall energy change is negative (energy is released to the surroundings), the reaction is exothermic.

Part (a)(i): 1 mark for endothermic. Part (a)(ii): 1 mark for reactants drawn at a lower level than products; 1 mark for vertical axis labeled energy and horizontal axis representing progress of reaction; 1 mark for curve with a peak above product level; 1 mark for activation energy clearly shown from reactant level to the peak. Part (b)(i): 1 mark for stating bond breaking is endothermic / takes in energy; 1 mark for stating bond making is exothermic / releases energy; 1 mark for stating more energy is released in bond making than is taken in during bond breaking. Part (b)(ii): 1 mark for calculating -600 kJ/mol (or 600 kJ/mol released); 1 mark for stating the reaction is exothermic.

Part (a)(i): Methane reacts with oxygen during complete combustion to form carbon dioxide and water: \(\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}\). Part (a)(ii): Carbon dioxide is a greenhouse gas that absorbs infrared radiation, contributing to global warming and global climate change. Part (b)(i): Under limited oxygen conditions, incomplete combustion produces carbon monoxide gas (CO) and solid carbon particles (soot, C). Part (b)(ii): Carbon monoxide is highly toxic because it is a colorless, odourless gas that binds strongly to haemoglobin in human red blood cells in place of oxygen. This drastically reduces the capacity of blood to carry oxygen to organs, which can lead to unconsciousness and death. Part (c): Coal contains sulfur impurities which react with oxygen during combustion to form sulfur dioxide (\(\text{SO}_2\)). This gas rises into the atmosphere and dissolves in water droplets in clouds, forming dilute sulfuric acid, which falls as acid rain.

Part (a)(i): 3 marks total: 1 mark for correct reactants (CH4 and O2); 1 mark for correct products (CO2 and H2O); 1 mark for correct balancing (2 O2 and 2 H2O). Part (a)(ii): 1 mark for greenhouse effect / global warming / climate change. Part (b)(i): 2 marks for carbon monoxide and carbon / soot (1 mark each). Part (b)(ii): 1 mark for stating it binds to haemoglobin in blood; 1 mark for stating it reduces or prevents oxygen transport around the body. Part (c): 1 mark for stating sulfur burns/reacts with oxygen to produce sulfur dioxide; 1 mark for explaining that sulfur dioxide dissolves in water/clouds to produce acid rain.

(a) Fractional distillation works by separating liquids with different boiling points. The oil is vaporised by heating, and the gaseous mixture enters the column. The temperature gradient (cool at top, hot at bottom) causes hydrocarbons with high boiling points to condense near the bottom, while those with lower boiling points rise higher and condense near the top.
(b) Greenhouse gases include carbon dioxide, methane, and water vapour.
(c)(i) Complete combustion always produces carbon dioxide and water: heptane + oxygen \(\rightarrow\) carbon dioxide + water.
(c)(ii) Incomplete combustion due to a lack of oxygen produces carbon monoxide (and/or soot/carbon).
(d) The standard test for carbon dioxide is to pass it through limewater (aqueous calcium hydroxide). Carbon dioxide reacts to form insoluble calcium carbonate, turning the solution cloudy.

Part (a) [4 marks]
- M1: Heat / vaporise the crude oil (before entering the column) (1)
- M2: Temperature gradient in the column / hotter at the bottom and cooler at the top (1)
- M3: Vapours rise up the column (1)
- M4: Fractions/hydrocarbons condense at different levels / heights depending on their boiling points (1)

Part (b) [2 marks]
- Any two from: carbon dioxide, methane, water vapour (1 mark each, max 2 marks)

Part (c)(i) [1 mark]
- Heptane + oxygen \(\rightarrow\) carbon dioxide + water (1) [Accept reactants and products in any order on their respective sides]

Part (c)(ii) [1 mark]
- Carbon monoxide (1) [Accept CO]

Part (d) [2 marks]
- Test: Bubble the gas through / add to limewater (1)
- Result: Turns cloudy / milky / white precipitate forms (1)

(a)(i) Sodium reacts vigorously with water. It floats because it is less dense than water, melts into a shiny ball due to the heat generated, and fizzes as hydrogen gas is produced.
(a)(ii) Alkali metals react with water to form a metal hydroxide and hydrogen gas: sodium + water \(\rightarrow\) sodium hydroxide + hydrogen.
(a)(iii) Going down Group 1, atoms get larger and have more electron shells. Sodium has 3 shells (2,8,1) while lithium has 2 shells (2,1). The single outer electron in sodium is further from the positively charged nucleus, resulting in a weaker electrostatic attraction, making it easier to lose during a reaction.
(b)(i) Bromine is a liquid at room temperature and is red-brown in colour.
(b)(ii) Chlorine is higher up in Group 7 than bromine, so it is more reactive. It displaces the less reactive bromide ions from potassium bromide to form potassium chloride and bromine. The formation of free bromine causes the colourless solution to turn orange-brown.

Part (a)(i) [1 mark]
- Any one observation from: floats / melts into a ball / fizzes or bubbles / moves around on the surface (1) [Do not accept 'catches fire with lilac flame' - this is for potassium]

Part (a)(ii) [2 marks]
- sodium hydroxide (1)
- hydrogen (1) [Accept in either order]

Part (a)(iii) [3 marks]
- M1: Sodium has more electron shells / outer electron is further from the nucleus (1)
- M2: Weaker electrostatic attraction between the nucleus and the outer electron (1)
- M3: Outer electron is lost more easily (1)

Part (b)(i) [2 marks]
- State: Liquid (1)
- Colour: Red-brown / orange-brown / brown (1)

Part (b)(ii) [2 marks]
- Explanation: Chlorine is more reactive than bromine (1)
- Colour change: (Turns from colourless to) orange / brown (1)